1. Field of the Invention
The invention relates to content distribution systems utilizing client-server architecture. In particular, the invention relates to a novel and improved dynamic control of content distribution polling.
2. Description of the Related Art
Increasing data transmission capacity of wireless networks, such as mobile telecommunication networks, has recently allowed downloading larger and larger files to mobile terminal devices more conveniently than ever. At the same time, increasing capabilities of the mobile terminal devices, such as higher processing power, larger storage resources and higher quality color displays, have allowed processing ever increasing amounts of information.
As a result, new services requiring large amounts of data to be transferred and processed have been made possible, such as various multimedia services which are growing in popularity.
As an example, there has recently been provided various content distribution services which typically allow downloading content, e.g. multimedia content, automatically to mobile terminal devices.
Often, these content distribution solutions are subscription based. That is, a user subscribes to a set of services for a given subscription period, e.g. 30 days, and all the content associated with the subscribed set of services is automatically delivered to a terminal device of the user during the subscription period.
The above automatic downloading is typically implemented by utilizing polling in a client-server architecture. That is, at given polling intervals, content distribution client software installed in the terminal device of the user sends a polling request message to a content distribution server inquiring whether there is new content, such as multimedia files, for downloading. In response, the content distribution server sends a polling response message to the content distribution client software which polling response message informs whether there is new downloadable content. If there is new downloadable content, the polling response message typically includes information about the download location of this new downloadable content after which the content distribution client software typically proceeds to download the new content automatically to the terminal device of the user. Consequently, the user may view the downloaded content at leisure. The download location may be at the polled server, or a separate server may be utilized for storage purposes.
Typically, when a user first subscribes to a set of services, a system administrator assigns a polling interval to the user. The polling interval indicates the frequency at which the content distribution client software sends polling request messages. The polling interval may be e.g. 15 minutes. Typically, the polling interval is client or user specific. In addition to the polling interval, a polling window is also often assigned to the user. The polling window indicates a time period when the content distribution client software may send polling request messages to the content distribution server. The polling window may be e.g. 9 p.m. to 7 a.m. Typically, the polling interval and the polling window are sent from the content distribution server to the content distribution client software when the user first subscribes to a set of services. Furthermore, the installation time of the content distribution client software typically serves as a starting point from which subsequent polling times will be determined. For example, if the content distribution client software was installed at 3.02 p.m., and the assigned polling window is from 9 p.m. to 7 a.m., and the assigned polling interval is 15 minutes, then the first polling time will be 9.02 p.m., the second polling time will be 9.17 p.m., and so on.
There is, however, a significant problem with the above described content distribution arrangement in regards to server overloading due to a sudden rush of polling request messages. A typical content distribution arrangement may include e.g. hundreds of users. In prior art, the polling request messages sent from all the terminal devices of these users are not synchronized in any way with each other. As a result, at one second, the content distribution server may receive a multitude of polling request messages. Yet, after a minute, there may be several tens of seconds without any polling request messages received. In other words, the load of the content distribution server receiving the polling request messages is not distributed evenly over time. Therefore, at times the content distribution server may not be able process incoming traffic which will result in instability of the content distribution arrangement.
As described above, the installation time of the content distribution client software to a given terminal device typically serves as a starting point from which subsequent polling times will be determined for that combination of content distribution client software and terminal device. Therefore, if for example ten clients are installed to the system at the same time, each of the clients will be assigned the same polling times. In addition, latency caused by e.g. network conditions between a content distribution client and the content distribution server or by the content distribution server being under heavy load or overloaded, may result in uncontrollable shifts in polling times.
FIG. 3a illustrates the above described prior art random distribution of polling times. Time block 300 comprises sub-blocks 301-320. Five clients have been assigned polling times in sub-block 302, five clients in sub-block 306, nine clients in sub-block 312, one clients in sub-block 313, three clients in sub-block 316, and four clients in sub-block 319. In other words, the polling times of the various clients are distributed randomly over the time block 300.
Therefore, the object of the present invention is to alleviate the problems described above and to introduce a solution that allows content distribution with polling instants of multiple clients distributed more uniformly over predetermined polling time slots.